JWM width in Slacko 5.4 only 1024 at 1366x768 resolution

[mdn]

I just tried installing Slacko 5.4 on a computer with a 1366x768 monitor, and the screen resolution was successfully set to something at least close to 1366x768, but the JWM panel and maximized windows were only about 1024 pixels wide, leaving a gap on the right side of the screen. Is there some way to get the window manager to recognize the 1366x768 resolution instead of treating it like 1024x768?

Added 3/6/2013: This bug seems to be related to the nouveau driver for NVidia video hardware. I saw something similar on Ubuntu 12.04 and worked around it there by switching to nv.